The Millennium:
A Space and Astronomy Timeline
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The Second Millennium (1001 - 2000AD)
    20th Century (1901 - 2000)

    The First Half of the 20th Century -- 1901-1950

      1900: German physicist Max Karl Ernst Ludwig Planck finds energy in packets he calls quanta and formulates quantum theory. He will win a 1918 Nobel Prize for discoveries in connection with quantum theory.

        1900s: Theoretical physicists rethink the microworld, adopting quantum mechanics based on the quantum theory of the structure and behavior of atoms and molecules.

      1901: American astronomer Annie Jump Cannon publishes a catalog classifying stellar spectra.

      1901: Italian engineer Guglielmo Marconi transmits long-wave wireless signals across the Atlantic Ocean. He will share the 1909 Nobel Prize in physics.

      1903: American aviation pioneers, the Wright brothers, Orville and Wilbur, fly the first powered, controlled, heavier-than-air plane at Kitty Hawk, N.C.

      1904: American astrophysicist George Ellery Hale founds the Mount Wilson Observatory in California. Construction begins on the Mount Wilson 100-inch telescope. Hale directs the observatory until 1923. Mount Wilson is a 5,710-ft.-high mountain in the San Gabriel Mountains of southwest California northeast of Pasadena.

      1904: A general theory of radioactivity is set forth by New Zealand-born British physicist Ernest Rutherford and British chemist Frederick Soddy. Rutherford classified radiation into alpha, beta, and gamma types and discovered the atomic nucleus-- the structure of the nuclear atom. He will win the 1908 Nobel Prize in chemistry. The rutherford, a unit expressing the rate of decay of radioactive material, is named for him. Soddy will win a 1921 Nobel Prize for investigations into the origin and nature of isotopes.

      1905: German-born American theoretical physicist Albert Einstein introduces his theory of special relativity and other key theories in physics on the photoelectric effect and Brownian motion. His special and general theories of relativity will revolutionize modern thought on the nature of space and time and form a theoretical base for the exploitation of atomic energy. He will win a 1921 Nobel Prize for his explanation of the photoelectric effect. At the end of the 20th century, he will be named Person of the Century by Time magazine.

      1905: American astronomer and pioneer in photography Edward Emerson Barnard uses a photographic telescope on California's Mount Wilson for seven months to picture the Milky Way.

      1906: Sound is broadcast over the wireless by Canadian-born engineer and inventor Reginald Aubrey Fessenden. His first radio broadcast combines voice and music.

      1908: A comet explodes over the Tunguska area of Siberia. Tunguska is the name of three rivers -- the Upper Tunguska, the Lower Tunguska and the Stony Tunguska.

      1908: Mount Wilson 60-inch reflector telescope begins in California.

      1910: Danish astronomer Ejnar Hertzsprung and American astronomer Henry Norris Russell publish their Hertzsprung-Russell diagram -- a graph of the absolute magnitude of stars plotted against their surface temperature or color. The diagram is used in the study of stellar evolution. Hertzsprung and Russell develop a theory of the evolution of stars.

      1910: The Great January Comet, visible in daylight, becomes the brightest of the century.

      1912: American astronomer Henrietta Swan Leavitt, stuyding variable stars in the Small Magellanic Cloud galaxy, describes the relationship of period and luminosity in Cepheid variables -- a regular cycle of variation in the brightness of certain stars.

      1913: Danish physicist Niels Henrik David Bohr postulates his theory of atomic structure. He will win a 1922 Nobel Prize for investigating atomic structure and radiations. His son, Aage Niels Bohr, also a physicist, will share a 1975 Nobel Prize for discovering the asymmetry of atomic nuclei.

      1915: Einstein publishes his Theory of General Relativity, offering a new explanation of gravity.

      1915: American astronomer Walter Sydney Adams spots the first white dwarf star, Sirius B. He develops a method of measuring the distance to a star from Earth by comparing its absolute brightness to its apparent brightness.

      1916: American astronomer and pioneer in photography Edward Emerson Barnard discovers Barnard's star, the second-nearest star system to the Sun.

      1917: Karl Schwarzschid suggests the existence of black holes that swallow matter.

      1918: American astronomer Harlow Shapley, discovering that our Solar System sits near the edge, and not in the middle, of our galaxy, says the Sun is a marginal star in a vast Milky Way. He will be remembered for his work in cosmology, spectroscopy, and photometry.

      1919: Mount Wilson 100-inch Hooker reflector telescope starts operation in California.

      1919: George Ritchey uses the Mount Wilson 60-inch telescope in California to locate faint light from erupting novae stars in spiral nebulae, suggesting that they were at extreme distances away from Earth.

      1919: British mathematician, astronomer, and physicist Arthur Stanley Eddington supports the theory of general relativity with photographs of a total solar eclipse. He is an early exponent of the theory of relativity who conducts research on the evolution, structure and motion of stars.

      1919: New Time Ball is installed on Greenwich Royal Observatory.

      1920: Frances Pease and John Anderson measure the diameter of the first star beyond the Sun, Betelgeuse.

      1923: American astronomer Edwin Powell Hubble identifies Cepheid variable stars in the Andromeda Nebula, galaxy M31, proving that the galaxy is more than one million lightyears from Earth and that other spirals of stars are far beyond our own Milky Way galaxy.

      1924: British physicist Edward Victor Appleton and Samuel Barnett discover the ionosphere. Appleton will win a 1947 Nobel Prize for his discovery of the F layer of the ionosphere.

      1925: National Geographic speculates about canals on Mars.

      1925: British-Scottish electrical engineer John Logie Baird transmits human features by television. He pioneers television, radar and fiber optics.

      1925: Cecilia Payne-Gaposchkin establishes a temperature scale for stellar atmospheres.

      1926: American physicist Robert Hutchings Goddard launches his first liquid fuel rocket. He invents numerous rocketry devices. NASA's Goddard Space Flight Center in Maryland will be named in his honor.

      1926: Bertil Lindblad says that galaxies rotate.

      1927: American electrical engineer Philo Taylor Farnsworth demonstrates working model of a television.

      1927: Belgian astrophysicist Georges Henri Lemaitre proposes a Big Bang theory for the origin of the Universe.

      1927: German physicist and one of the founders of quantum mechanics Werner Karl Heisenberg describes the uncertainty principle. He will win a 1932 Nobel Prize for the uncertainty principle.

      1928: British mathematician and physicist Paul Adrien Maurice Dirac suggests the existence of antimatter. He will share a 1933 Nobel Prize for his new formulations of the atomic theory.

      1929: Hubble, calculating the distances to galaxies, makes what has been called the most important astronomical discovery of the 20th century and proposes a theory of an expanding Universe, saying galaxies recede from each other in an expanding Universe. The velocities of nebulae increase with distance. That seems to imply that all matter in the Universe once was compacted together in a very small space. That suggests that it all exploded from a definite point in a Big Bang ten to fifteen billion years ago.

      1929: Russell shows that Deep Space contains mostly hydrogen, which fuels the stars.

      1930: The planet Pluto is found by American astronomer Clyde William Tombaugh.

      1930: Robert Trumpler at the Lick Observatory proves there are dust clouds along the Milky Way.

      1930: Indian-born American astrophysicist Subrahmanyan Chandrasekhar defines the struture and mass limit of white dwarf stars. He will share a 1983 Nobel Prize for research on the evolution of stars.

      1930: Bernhard Schmidt invents the Schmidt camera.

      1930: Austrian-born American physicist Wolfgang Pauli theorizes the existence of neutrinos. He will win a 1945 Nobel Prize for work on atomic fissions.

      1930: A cyclotron is developed by American physicist Ernest Orlando Lawrence. The cyclotron is a circular particle accelerator in which charged subatomic particles are accelerated spirally outward in a magnetic field. It can generate energies up to tens of millions of electron volts. Lawrence will win a 1939 Nobel Prize for development of the cyclotron.

      1931: Bell Telephone Laboratories engineer Karl Jansky, looking for the cause of radio static, is the first person to tune in radio waves coming from somewhere in the sky. He founds radioastronomy by detecting radio waves coming from the center of our Milky Way galaxy.

      1932: American astronomer Walter Sydney Adams and Theodore Dunham discover a thick carbon dioxide atmosphere around the planet Venus.

      1932: British physicist James Chadwick discovers the neutron. He will win a 1935 Nobel Prize for his discovery.

      1932: The first bit of antimatter, the positron or antielectron, is uncovered by American physicist Carl David Anderson. He will win a 1936 Nobel Prize for his discovery.

      1934: German-born American astronomer Walter Baade and Fritz Zwicky predict that supernovas would produce neutron stars. Baade's research also led to more accurate measurement of interstellar distances.

      1937: Amateur radio operator Grote Reber of Wheaton, Illinois, becomes the father of the radiotelescope by building a 31-ft. dish antenna in his backyard and using it to uncover the first discrete radio sources beyond Earth and mapping the spread of natural radio signals across the Milky Way.

      1937: Fritz Zwicky demonstrates that most of the matter in the Coma Cluster of galaxies is invisible.

      1938: American filmmaker and actor George Orson Welles's makes the radio broadcast War of the Worlds.

      1938: German-born American physicist Hans Albrecht Bethe sets forth his theory of fusion reactions in stars, explaining the carbon cycle. He will win a 1967 Nobel Prize for research on the energy production of stars.

      1939: Construction begins on Mount Palomar's 200-in. Hale reflecting telescope. Mount Palomar is a 6,126-ft.-high peak in southern California northeast of San Diego. When the Hale is completed, the observatory will have one of the world's largest reflecting telescopes.

      1940s: The Second World War stimulates many inventions, including radar and other electronic technologies which stimulated radioastronomy after the war.

      1940: Gerard Kuiper discovers the atmosphere around Saturn's moon Titan.

      1942: The nuclear reactor is invented as Italian-born American physicist Enrico Fermi achieves the first controlled artificial nuclear chain reaction in his atomic pile in a squash court at the University of Chicago. He already had won a 1938 Nobel Prize for his work on artificial radioactivity caused by neutron bombardment. The fermi, a unit of length, is named in his honor.

      1945: The general-purpose digital computer is invented with the first electronic computer, ENIAC, at the University of Pennsylvania.

      1945-46: British radio astronomer Alfred Charles Bernard Lovell at Jodrell Bank Observatory in England and British astronomer Martin Ryle at Cambridge University develop the science of radioastronomy. Ryle will share a 1974 Nobel Prize for physics for using radio telescopes to probe outer space with great precision.

      1946: Martin Ryle discovers the first and brightest radio source beyond our galaxy, Cygnus A.

      1947: U.S. Air Force pilot Chuck Yeager in the X-1 becomes first person to break the sound barrier.

      1948: The 200-in. Hale reflecting telescope, one of the world's largest, opens on Mount Palomar in southern California northeast of San Diego.

      1948: Gerard Kuiper discovers Uranus' moon Miranda. Among Uranus' moons, Miranda is closest to the planet. It is named after the daughter of the magician Prospero in Shakespeare's The Tempest.

      1948: The transistor is invented by physicists at Bell Laboratories. It makes small radios and computers commercially feasible. A transistor is a tiny semiconductor electronic device used in a circuit as an amplifier, detector or switch. The word transistor is short for trans(fer) (res)istor.

      1948: Mount Palomar's 200-in. Hale telescope is dedicated.

      1948: Ralph Alpher and Robert Herman predict that cosmic background radiation will be found.

      1948: English astronomer, cosmologist and astrophysicist Fred Hoyle begins investigating the steady-state theory, which assumes the continuous creation of matter. Although the discovery of background radiation will negate his concept, Hoyle's ideas touch on fundamental cosmological problems and place him in the midst of controversy.

      1949: The first two-stage rocket launches at White Sands, New Mexico, proving grounds.

      1949: Gerard Kuiper discovers Neptune's moon Nereid-- the satellite third in distance from the planet. It is named for the sea nymphs who are the 50 daughters of Nereus in Greek mythology.

      1949-1956: Palomar Observatory Sky Survey photographs the entire visible sky with the observatory's 48-inch telescope in in southern California northeast of San Diego, locating millions of previously-unknown stars and galaxies.

      1950: Dutch astronomer Jan Hendrix Oort says that long-period comets come from a large reservoir of such bodies -- the Oort Cloud. The cloud is a swarm of comets orbiting the Sun at the far outer reaches of our Solar System at a distance of one to two lightyears. Comets from the cloud travel into the inner Solar System and then travel back out over long periods of time.

      1950: Fred Hoyle is skeptical of the theory that the Universe originated in a singular explosion -- the Big Bang. Hoyle champions the steady-state theory of the nature of the Universe. He has made significant contributions to the study of stellar evolution.

      Continue on to the years 1951-2000

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